fx
A tiny, open, model-agnostic coding agent CLI written in Zig, with an interface closer to a Unix shell than an IDE, embeddable as a harness in larger systems.
fx is a coding agent command-line tool written in Zig: a small native binary that is open source, model-agnostic, and embeddable as a harness inside larger systems. Its interface stays closer to a Unix shell than an IDE-in-the-terminal, with inline rendering that preserves normal terminal scrollback.
It can use models through the Vercel AI Gateway, a ChatGPT or Grok subscription, or any OpenAI-compatible endpoint such as Ollama or OpenRouter, and it can be used as an interactive shell, a one-shot ask command for scripts, or embedded through a library and the Agent Client Protocol. It supports skills, MCP servers and subagents, and custom named model connections can be added for local servers or gateways in a settings file, selected per profile or per invocation. When a model is served through the Vercel AI Gateway by more than one underlying provider, fx can direct which provider the gateway uses.
It installs with a shell script and is released under the Apache 2.0 license.